Aqueous polyurethane dispersions which can be hardened with mit UV-radiation and thermally, and use thereof

ABSTRACT

UV- and heat-curable aqueous polyurethane dispersions comprise compounds attached via polyisocyanates and containing UV-polymerizable C═C double bonds, aliphatic diols incorporated by way of isocyanates and having a molecular weight of less than 500 g/mol, compounds attached via isocyanates and containing carboxylic acid or sulfonic acid groups and/or salts thereof, free hydroxyl groups, and compounds containing blocked isocyanate groups. They are suitable for coating heat-stable substrates such as metal substrates and may be used with advantage for automotive clearcoats.

The invention relates to UV- and heat-curable polyurethane dispersionswhich have UV-polymerizable C═C double bonds, hydroxyl groups andblocked isocyanate groups in one molecule or the blocked isocyanategroups in admixed compounds, and to processes for their preparation anduse.

Radiation-curable polyurethane dispersions are known, for example, fromthe Applicant's DE-A 4434554 and are prepared from polyisocyanates,hydroxyl-containing polyesters, compounds containing anisocyanate-reactive group and an acid group, and compounds containing anisocyanate-reactive group and C═C double bonds. In terms of theirprocessing properties, however, the products leave a certain amount tobe desired. U.S. Pat. No. 5,859,135 describes aqueous coating mixturescomprising a lipophilic polymer containing at least one hydroxyl group,having a molecular weight of up to 100,000, which is connected on oneside to a crosslinkable functional group and on the other side, via apolyisocyanate, to a group containing carboxyl groups and to ahydrophilic polyalkylene oxide monoether radical.

A disadvantage is that coatings produced therewith have a relativelyhigh intrinsic hydrophilicity, even after processing. U.S. Pat. No.5,296,529 describes a self-crosslinking resin containing carboxyl,hydroxyl, and blocked isocyanate groups, which is prepared from a) acopolymer of a vinyl monomer containing free and blocked isocyanategroups with a styrene and/or (meth)acrylate comonomer, and b) apolyester resin containing hydroxyl and carboxyl groups, some hydroxylgroups of the polyester resin being reacted with some free isocyanategroups of the vinyl copolymer, and remaining isocyanate groups thenbeing blocked. It can be seen that a highly reproducible production ofthe system counters the risk of a premature unwanted crosslinking of thetwo polymers. Also, the system described contains no UV-curable doublebonds, nor is any radiation curing thereof described.

DE-A-198 60 041 describes reaction products of a) polyisocyanates and b)low molecular mass hydroxy compounds containing C═C double bonds, suchas hydroxyalkyl(meth)acrylates or hydroxyalkyl vinyl ethers, themajority of which constitute allophanates of the polyisocyanates withthe unsaturated alcohols. The low molecular mass reaction products,which are of low viscosity, have a high polymerizable C═C double bondcontent in the molecule and can be both polymerized with UV radiationand cured thermally, with the participation of the isocyanate groups, orby exposure to water vapor, ammonia, or amines. An application in theform of aqueous dispersions is not described.

It is an object of the present invention to prepare both UV- andheat-curable aqueous polyurethane dispersions which give rise tocoatings having good chemical resistance and good mechanical properties,in particular a high scratch resistance, which dry physically aftertreatment even at unexposed areas, and are suitable for exteriorapplications such as for an automobile finish.

We have found that this object is achieved with polyurethane dispersionssynthesized essentially from

a) aliphatic polyisocyanates having an NCO functionality of from 2 to4.5,

b) compounds containing at least one isocyanate-reactive group and atleast one UV-polymerizable C═C double bond,

c) aliphatic and/or cycloaliphatic compounds containing at least twohydroxyl, mercapto and/or primary and/or secondary amino groups, havinga molecular weight of less than 500 g/mol,

d) compounds containing at least one isocyanate-reactive group and alsoat least one carboxyl group or sulfonic acid group,

e) at least one basic compound for full or partial neutralization of theacid groups of the compounds d),

f) an isocyanate blocking agent (f1) which converts isocyanate groupsinto blocked isocyanate groups with an unblocking temperature in therange from 70 to 160° C., or addition of a compound (f2) containingblocked isocyanate groups, and

g) if desired, a compound different than compounds b) to f) whichcontains only one isocyanate-reactive group,

the reaction products of a) with b) and, if appropriate, c), preparedwith a stoichiometric excess of NCO groups in relation to the OH groups,having been reacted with compounds d) and e) in amounts sufficient fordispersibility in aqueous medium, isocyanate groups having beenconverted into blocked isocyanate groups by reaction with isocyanateblocking agents (f1), or compounds containing blocked isocyanate groups(f2) having been added.

The building blocks of the polyurethane dispersion:

Component a)

Aliphatic polyisocyanates a) having an NCO functionality of from 2 to4.5 and preferably from 2.0 to 3.5 include especially, as aliphatic(including cycloaliphatic)diisocyanates, hexamethylene diisocyanate,1,3- and 1,4-bis(isocyanatomethyl)cyclohexane, isophorone diisocyanate,and di(isocyanatocyclohexyl)methane. Preference is given topolyisocyanates having a functionality of at least 3, such aspolyisocyanates containing isocyanurate groups, biuret groups, uretdionegroups or urethane groups and/or allophanate groups. The polyisocyanatescontaining isocyanurate groups comprise, in particular, simpletrisisocyanato isocyanurates, which constitute cyclic trimers of thediisocyanates, or mixtures thereof with their higher homologs containingmore than one isocyanurate ring. The isocyanato isocyanurates generallyhave an NCO content of from 10 to 30, in particular from 15 to 25% byweight, and an average NCO functionality of 3 to 4.5. Polyisocyanatescontaining biuret groups are adducts of 3 molecules of diisocyanate with1 molecule of water and have in particular an NCO content from 18 to 22%by weight and an average NCO functionality of from 3 to 4.5.Polyisocyanates containing urethane groups and/or allophanate groups maybe obtained, for example, by reacting excess amounts of diisocyanatewith simple alcohols such as trimethylolpropane, glycerol,1,2-dihydroxypropane or mixtures thereof, for example, and generallyhave an NCO content of from 12 to 20% by weight and an average NCOfunctionality of from 2.5 to 3. Polyisocyanates having an NCOfunctionality of more than 2 that may be mentioned also include theadducts of 3 mol of diisocyanates such as isophorone diisocyanate withtrihydric alcohols such as trimethylolpropane.

The component a) preferably comprises at least one compound Va) havingtwo free isocyanate groups, at least one allophanate group, and at leastone free-radically polymerizable C═C double bond, a carbonyl group or anoxygen atom in ether function being attached directly to the doublebond.

The compound Va) is preferably selected from compounds of the formula I

 OCN—R¹R²—C(O)—R²—R¹_(n)NCO  (I)

where

n is an integer from 1 to 10,

R¹ is a divalent aliphatic or alicyclic C₂ to C₂₀ hydrocarbon unit or anaromatic C₆ to C₂₀ hydrocarbon unit,

R² in each repeating unit is once —NH— and once

 R³ being a radical derived from an alcohol A by abstracting thehydrogen atom from the alcoholic hydroxyl group, said alcohol A furthercomprising at least one free-radically polymerizable C═C double bond,and a carbonyl group or an oxygen atom in ether attachment beingattached directly to the double bond.

The radicals R¹ preferably comprise those derived by abstracting theisocyanate group from customary aliphatic or aromatic polyisocyanates.The diisocyanates are preferably aliphatic isocyanates having 4 to 20carbon atoms. Examples of customary diisocyanates are aliphaticdiisocyanates such as tetramethylene diisocyanate, hexylmethylenediisocyanate, octamethylene diisocyanate, decamethylene diisocyanate,dodecamethylene diisocyanate, tetradecamethylene diisocyanate,derivatives of lysine diisocyanate, tetramethylxylylene diisocyanate,cycloaliphatic diisocyanates such as 1,4-, 1,3- or1,2-diisocyanatocyclohexane, 4,4′- or2,4′-di(isocyanatocyclohexyl)methane, isophorone diisocyanate, 1,3- or1,4-bis(isocyanatomethyl)cyclohexane, 2,4- and2,6-diisocyanato-1-methylcyclohexane, and also aromatic diisocyanatessuch as 2,4- or 2,6-tolylene diisocyanate, m- or p-xylylenediisocyanate, 2,4′- or 4,4′-diisocyanatodiphenylmethane, 1,3- or1,4-phenylene diisocyanate, 1-chloro-2,4-phenylene diisocyanate,1,5-naphthylene diisocyanate, diphenylene 4,4′-diisocyanate,4,4′-diisocyanato-3,3′-dimethyldiphenyl diisocyanate,3-methyldiphenylmethane 4,4′-diisocyanate, and diphenyl ether4,4′-diisocyanate. Mixtures of the abovementioned diisocyanates may bepresent. Preference is given to hexamethylene diisocyanate,1,3-bis(isocyanatomethyl)-cyclohexane, isophorone diisocyanate, tetramthylxylylene diisocyanate, and di(isocyanatocyclohexyl)methane.

The alcohols A from which the radical R³ is derived comprise, forexample, esters of α,β-unsaturated carboxylic acids, such as acrylicacid, methacrylic acid (below for short “(meth)acrylic acid”), crotonicacid, acrylamidoglycolic acid, methacrylamidoglycolic acid orvinylacetic acid and polyols having preferably 2 to 20 carbon atoms andat least 2 hydroxyl groups, such as ethylene glycol, diethylene glycol,triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol,dipropylene glycol, tripropylene glycol, 1,4-butanediol,1,5-pentanediol, neopentyl glycol, 1,6-hexanediol,2-methyl-1,5-pentanediol, 2-ethyl-1,4-butanediol,1,4-dimethylolcyclohexane, glycerol, trimethylolethane,trimethylolpropane, trimethylolbutane, penta-erythritol,ditrimethylolpropane, erythritol and sorbitol, provided the ester has atleast one isocyanate-reactive OH group. The radicals R³ may also bederived from the amides of (meth)-acrylic acid with amino alcohols, e.g.2-aminoethanol, 3-amino-1-propanol, 1-amino-2-propanol or2-(2-aminoethoxy)-ethanol, and the vinyl ethers of the abovementionedpolyols, provided they still have one free OH group.

Also suitable as reactive components, furthermore, are unsaturatedpolyetherols or polyesterols or polyacrylate polyols having an averageOH functionality of from 2 to 10.

The radicals R³ are preferably derived from alcohols such as2-hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate,1,4-butanediol mono(meth)acrylate, neopentyl glycol mono(meth)acrylate,glycerol mono- and di(meth)acrylate, trimethylolpropane mono- anddi(meth)acrylate, and penta-erythritol di- and tri(meth)acrylate. Withparticular preference, the alcohol A is selected from 2-hydroxyethylacrylate, 2-hydroxyethyl methacrylate and hydroxypropyl(meth)acrylate.Examples of amides of ethylenically unsaturated carboxylic acids withamino alcohols are hydroxyalkyl(meth)acrylamides such asN-hydroxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide,5-hydroxy-3-oxopentyl(meth)acrylamide, N-hydroxyalkylcrotonamides suchas N-hydroxymethylcrotonamide or N-hydroxyalkylmaleimides such asN-hydroxyethylmaleimide.

In particular the component a) comprises at least one compound Va) andat least one further, different aliphatic or araliphatic polyisocyanate.Preferred further polyisocyanates are polyisocyanates having an NCOfunctionality of from 2 to 4.5, with particular preference from 2 to3.5. It is preferred to use aliphatic, cycloaliphatic, and araliphaticdiisocyanates. These include, for example, tetramethylene diisocyanate,hexamethylene diisocyanate, 2,3,3-trimethylhexamethylene diisocyanate,1,4-cyclohexylene diisocyanate, isophorone diisocyanate, 1,3- and1,4-bis(isocyanatomethyl)cyclohexane, di(isocyanatocyclohexyl)methane,tetramethylxylylene diisocyanate, and mixtures thereof. Preference isgiven to polyisocyanates containing not only two or more isocyanategroups but also a group selected from the group of the urethane, urea,biuret, allophanate, carbodiimide, uretonimine, uretdione, andisocyanurate groups. Preferred additional polyisocyanates are isophoronediisocyanate, 1,3- and 1,4-bis(isocyanatomethyl)cyclohexane, theirisocyanurates, biurets and allophanates, and mixtures thereof.

Particularly preferred polyisocyanate starting materials for preparingthe curable polyurethane dispersions of the invention areallophanate-group-containing polyisocyanates of hexamethylenediisocyanate or of isophorone diisocyanate with the hydroxy compounds b)containing C═C groups, as described in DE-A-198 60 041, and especiallythe corresponding reaction products of the polyisocyanates with thehydroxyalkyl (meth)acrylates.

Component b)

The compounds of component b) generally contain a free-radicallypolymerizable C═C double bond and also at least one otherisocyanate-reactive group. Examples of preferred compounds of componentsb) are the monoesters of dihydric or polyhydric alcohols withα,β-ethylenically unsaturated mono- and/or dicarboxylic acids and theiranhydrides. α,β-Ethylenically unsaturated mono- and/or dicarboxylicacids and their anhydrides which may be used include, for example,acrylic acid, methacrylic acid, fumaric acid, maleic acid, maleicanhydride, crotonic acid, itaconic acid, etc. It is preferred to useacrylic acid and methacrylic acid. Examples of suitable alcohols arediols such as glycols, preferably glycols of 2 up to 25 carbon atoms,such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol,1,5-pentanediol, 1,4-pentanediol, 1,6-hexanediol, 1,10-decanediol,diethylene glycol, etc. Suitable triols and polyols have, for example, 3to 25, preferably 3 to 18, carbon atoms. Examples include glycerol,trimethylolpropane, erythritol, pentaerythritol, sorbitol, etc. Thecompounds of component b) are selected preferably from 2-hydroxyethylacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate,2-hydroxypropyl methacrylate, 3-hydroxybutyl acrylate, 3-hydroxybutylmethacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate,6-hydroxyhexyl acrylate, 6-hydroxyhexyl methacrylate,3-hydroxy-2-ethylhexyl acrylate, 3-hydroxy-2-ethylhexyl methacrylate,trimethylolpropane monoacrylate and mixtures thereof. If desired, thesecompounds may also have been chain-extended by reaction with anappropriate chain extender, such as a polyfunctional isocyanate or apolyfunctional carboxylic acid, for example.

Further suitable compounds b) are the esters and amides of aminoalcohols with the abovementioned α,β-ethylenically unsaturated mono-and/or dicarboxylic acids, hydroxyalkyl vinyl ethers such ashydroxybutyl vinyl ether, etc.

Particularly suitable compounds b) containing at least oneisocyanate-reactive group and also at least one C═C double bondpolymerizable with UV radiation in the presence of a photoinitiator aremethacrylic monoesters and acrylic monoesters of aliphatic diols andalso methacrylamides and acrylamides of amino alcohols, and,furthermore, hydroxyalkyl vinyl ethers such as hydroxybutyl vinyl ether,of which preference is given to hydroxyalkyl acrylates having 2 to 4carbon atoms in the alkyl radical, such as 2-hydroxyethyl acrylate,where the adjacent carbonyl group or ether group contributes toactivating the C═C double bond.

Component c)

For the preparation of the polyurethane it is advantageous to usefurther aliphatic compounds c) containing at least twoisocyanate-reactive hydroxyl, mercapto and/or amino groups and having amolecular weight of less than 500 g/mol. Particularly suitable suchcompounds are hydrolytically stable short-chain diols such asdihydroxymethylcyclohexane, bis(hydroxycyclohexyl)-propane,tetramethylcyclobutanediol, cyclooctanediol, or norbornanediol.Preference is given to the use of hydrocarbon diols having a C number offrom 6 to 20, such as hexanediol, octanediol, decanediol, ordodecanediol.

The additional use of polyfunctional alcohols, amino alcohols or thioalcohols may also serve, however, to introduce isocyanate-reactivefunctional groups prior to final curing, if the stoichiometry is chosenso that statistically only a few of the isocyanate-reactive groups reactin reactions prior to final curing. To accelerate the reaction of thepolyisocyanates it is possible to use the customary catalysts such asdibutyltin dilaurate, tin(II) octoate, or diazabicyclo[2.2.2]octane. Inthe preparation of allophanates of the polyisocyanates with theunsaturated alcohols at temperatures of from 20 to 280° C., the presenceof catalysts which promote allophanate formation is advantageous, suchas organozinc compounds or tetraalkylammonium compounds. Regarding thepreparation of the allophanates, reference may be made again to theremarks in DE-A-198 60 041.

Component d)

Particularly suitable compounds d) containing at least oneisocyanate-reactive group and also at least one carboxylic acid orsulfonic acid group are aliphatic monomercapto-, monohydroxy- andmonoamino- and iminocarboxylic acids and corresponding sulfonic acids,such as mercaptoacetic acid (thioglycolic acid), mercaptopropionic acid,mercaptosuccinic acid, hydroxyacetic acid, hydroxypivalic acid,dimethylolpropionic acid, hydroxydecanoic acid, hydroxydodecanoic acid,12-hydroxystearic acid, hydroxyethanesulfonic acid,hydroxypropanesulfonic acid, mercaptoethanesulfonic acid,mercaptopropanesulfonic acid, aminopropanesulfonic acid, glycine(aminoacetic acid), or iminodiacetic acid.

Component e)

Suitable basic compounds e) for full or partial neutralization of theacid groups of the compounds include organic and inorganic bases such asalkali metal and alkaline earth metal hydroxides, oxides, carbonates,hydrogen carbonates, and also ammonia or primary, secondary, or tertiaryamines. Preference is given to full or partial neutralization withamines such as with ethanolamine or diethanolamine and in particularwith tertiary amines, such as triethylamine, triethanolamine,dimethylethanolamine, or diethylethanolamine. The amounts of chemicallybonded acid groups introduced and the extent of the neutralization ofthe acid groups (which is usually from 40 to 100% of the equivalencebasis) should be sufficient to ensure dispersion of the polyurethanes inan aqueous medium, as is familiar to the skilled worker.

Component f)

Suitable blocking agents for isocyanate groups (f1) are compounds whichconvert the isocyanate groups into blocked isocyanate groups whichsubsequently below their unblocking temperature do not exhibit thecustomary reactions of a free isocyanate group. When the blockedisocyanate groups are heated to a temperature which corresponds at leastto the unblocking temperature, which for the purposes of this inventionis to be situated within the range from 70 to 160° C., the isocyanategroups are exposed again and are available for customary isocyanatereactions, for example, for reactions with functional groups such ashydroxyl, mercapto, or amino groups, for example. Compounds which block(cap, mask or protect) the isocyanate groups have been widely describedin the literature (cf., e.g., Z. W. Wicks, Prog. Org. Coat. 3(1975)73-99 and also 9(1981) 3-28 or Houben-Weyl, Methoden der OrganischenChemie Vol. XIV/2, p. 61 ff., Georg Thieme Verlag, Stuttgart 1963).Typical blocking agents of isocyanate groups (f1) are phenols,caprolactam, imidazoles, pyrazoles, pyrazolinones, 1,2,4-triazoles,diketopiperazines, malonates, and oximes. Preference is given to oximessuch as 2-butanone oxime, 3,5-dimethylpyrazole, and 1,2,4-triazoles.Instead of blocking isocyanate groups in the same molecule with theblocking agent, which is preferred, an alternative is to admix to thepolyurethane a low molecular mass compound containing blocked isocyanategroups (f2), which subsequently, in the course of curing, with heatingto at least the unblocking temperature, exposes reactive isocyanategroups and is available for the curing or crosslinking reaction. It isalso possible to use mixtures of isocyanate blocking agents havingdifferent unblocking temperatures within the aforementioned range.

Component g)

Finally, it is possible to use compounds g) which are different than thecompounds b) to f) and have only one isocyanate-reactive group, inorder, for example, to modify the properties of the polyurethane and/orto reduce the number of reactive free isocyanate groups.

In order to modify the polyurethane dispersions of the invention theymay be admixed conventionally with reactive diluents, as described inP.K.T. Oldring (Editor), Chemistry & Technology of UV & EB Formulationsfor Coatings, Inks & Paints, Vol. II, Chapter III: Reactive Diluents forUV & EB Curable Formulations, Wiley and SITA Technology, London 1997. Inaccordance with a first embodiment, the reactive diluents are to containno hydroxyl groups. Preferred reactive diluents are esters of acrylicacid which are derived from diols or polyols, preferably aliphaticpolyhydric polyalcohols and alkoxylation products thereof. Examples ofvery suitable reactive diluents which may also be used for a furtherincrease in hardness of the coatings produced with the polyurethanedispersions are, for example, trimethylolethane tri(meth)acrylate,trimethylolpropane tri(meth)acrylate, or pentaerythritoltetra(meth)acrylate. Preference is also given to hexanediol diacrylate,hexanediol dimethacrylate, octanediol diacrylate, octanedioldimethacrylate, nonanediol diacrylate, nonanediol dimethacrylate,decanediol diacrylate, and decanediol dimethacrylate. Further suitablecompounds are the esters of alicyclic diols, such as cyclohexanedioldi(meth)acrylate and bis(hydroxymethylethyl)cyclohexanedi(meth)acrylate. Other suitable reactive diluents includetrimethylolpropane monoformal acrylate, glycerol formal acrylate,4-tetrahydropyranyl acrylate, 2-tetrahydropyranyl methacrylate andtetrahydrofurfuryl acrylate.

In accordance with another embodiment, the reactive diluents have atleast two functional groups, selected from free-radically polymerizabledouble bonds and isocyanate-reactive groups. They include, on the onehand, polymeric polyols other than component c). The number-averagemolecular weight M_(n) of these polymers is preferably situated within arange from about 1000 to 100,000, with particular preference from 2000to 10,000. The OH numbers are preferably within a range from about 40 to200 mg KOH/g polymer. Preferred polymers are, for example, copolymerscontaining in copolymerized form at least one of the abovementionedmonoesters of dihydric or polyhydric alcohols with at least oneα,β-ethylenically unsaturated mono- and/or dicarboxylic acid and atleast one further comonomer selected preferably from vinylaromaticcompounds, such as styrene, for example, esters of the abovementionedα,β-unsaturated mono- and/or dicarboxylic acids with monoalcohols, vinylesters of carboxylic acids containing up to 20 carbon atoms, vinylhalides, nonaromatic hydrocarbons having 4 to 8 carbon atoms and 1 or 2double bonds, unsaturated nitrites, etc., and mixtures thereof. Theyfurther include (partially) hydrolyzed vinyl ester polymers, preferablypolyvinyl acetates. They additionally include polyesterols based onaliphatic, cycloaliphatic and/or aromatic di-, tri- and/orpolycarboxylic acids with di-, tri- and/or polyols and alsolactone-based polyesterols. They additionally include polyetherolsobtainable by polymerizing cyclic ethers or by reacting alkylene oxideswith a starter molecule, and also α,ω-diamino polyethers obtainable byreacting polyetherols with ammonia. Moreover, they also includecustomary polycarbonates known to the skilled worker and containingterminal hydroxyl groups, which are obtainable, for example, by reactingthe aforementioned diols with phosgene or carbonic diesters.

Suitable reactive diluents containing at least one free-radicallypolymerizable C═C double bond and at least one isocyanate-reactive groupare the esters and polyesters of the aforementioned α,β-ethylenicallyunsaturated mono- and/or dicarboxylic acids with diols or polyols thatstill contain free hydroxyl groups. They include, for example,pentaerythritol diacrylate, dipentaerythritol tetraacrylate,dipentaerythritol triacrylate, etc. Also suitable are the esters, againstill containing free hydroxyl groups, of alkoxylated polyols withα,β-ethylenically unsaturated mono- and/or dicarboxylic acids, such asthe acrylates or methacrylates of alkoxylated trimethylolpropane,glycerol, or pentaerythritol, for example.

The coating compositions of the invention may be prepared from theindividual components described and by the above instructions inaccordance with techniques customary to the skilled worker, possiblyusing known coating additives, such as leveling agents, defoamers, UVabsorbers, dyes, pigments and/or fillers.

The polyurethane content of the aqueous dispersions may be in particularbetween 5 and 70 and in particular between 20 and 50% by weight, thesolids content being determined gravimetrically.

Prior to the curing of the polyurethane dispersions with UV radiation,it is advantageous to add to them photoinitiators in an amount of from0.01 up to 10 and preferably from 1 to 5% by weight, based on the solidscontent of the dispersion, these photoinitiators being as specified inPatent Application DE-A-198 60 041.

Examples hereof include benzophenone and benzophenone derivatives, suchas 4-phenylbenzophenone and 4-chlorobenzophenone, Michler's ketone,acetophenone derivatives, such as 1-benzoylcyclohexan-1-ol,2-hydroxy-2,2-dimethylacetophenone, and2,2-dimethoxy-2-phenylacetophenone, benzoin and benzoin ethers, such asmethyl, ethyl and butylbenzoin ethers, benzil ketals, such as benzildimethyl ketal,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,anthraquinone and its derivatives, such as methylanthraquinone andtert-butylanthraquinone, acylphosphine oxides, such as2,4,6-trimethylbenzoyldiphenylphosphine oxide, ethyl2,4,6-trimethylbenzoylphenylphosphinate, methyl2,4,6-trimethylbenzoylphenylphosphinate and bisacylphosphine oxides.

For particular preference the dispersions of the invention include atleast one photoinitiator selected from phenylglyoxalic acid and theesters and salts thereof. Particular preference is given to compounds ofthe formula I

R¹ is a hydrogen atom or a C₁-C₁₈ alkyl group. Preferably, R¹ is a C₁-C₈alkyl group, especially methyl, ethyl, propyl, butyl, or hexyl.

R² and R³ independently of one another are a hydrogen atom or a C₁-C₁₈alkyl or C₁-C₁₈ alkoxy group.

Preferably R² and R³ independently of one another are a hydrogen atom.

Where at least one of the two radicals R² and R³ is other than ahydrogen atom, the phenyl ring is substituted preferably para (inposition 4) to the carbonyl group.

Particular preference is also given to phenylglyoxalic esters of theformula II

where the two radicals R⁴ independently of one another are a radical ofthe formula

R⁵, RS and R⁷ independently of one another are H, C₁-C₆ alkylunsubstituted or substituted by OH, OC₁-C₆ alkyl or OCOC₁-C₆ alkyl, orare OH or OC₁-C₆ alkyl;

A is C₂-C₆ alkylene or a radical of the formulae

the radicals R⁸ independently of one another are H or COCOR⁴, and A¹ isC₂-C₆ alkylene or

Compounds of this kind are described in DE-A-198 26 712 and GermanPatent Application P-199 13 353.0, the entirety of which is incorporatedhere by reference. Preferably, the above-described photoinitiators basedon phenylglyoxalic acid derivatives are suitable for exteriorapplications, since they show little or no yellowing.

In accordance with one suitable embodiment, the dispersions of theinvention further comprise at least one thermal initiator. Preferredthermal initiators are those having a half-life at 60° C. of at leastone hour, preferably at least two hours. The half-life of a thermalinitiator is the time at which half of the initial amount of theinitiator has undergone decomposition into free radicals. On a substratecoated with a dispersion of the invention, these initiators generallypermit the formation of a film by customary methods, such as evaporationwith heating, for example, at which point essentially no thermalinitiation and curing yet takes place.

The thermal initiator component is used preferably in an amount of from0.1 to 10% by weight, more preferably from 0.5 to 5% by weight, based onthe total amount of components a) to g).

Suitable thermal initiators are, generally, all compounds which undergodecomposition into free radicals under the curing conditions, such as,for example, peroxides, hydroperoxides, hydrogen peroxides, persulfates,azo compounds, highly substituted—e.g., hexasubstituted—ethanes, amineN-oxides, redox catalysts, etc. Preference is given to the use ofwater-soluble initiators. Examples of suitable thermal initiators aretriphenylmethylazobenzene, benzoyl peroxide, di-tert-butyl peroxide,cumene hydroperoxide, dicumyl peroxide, tert-butyl perbenzoate,2,2,6,6-tetramethylpiperidin-1-yloxy, benzpinacol and derivativesthereof.

The thermal initiator component further comprises, preferably, at leastone thermal initiator containing at least one isocyanate-reactive group,the initiator also being capable, after reaction with a compoundcontaining isocyanate groups, of releasing free radicals under heat.These include, for example, initiators containing at least one bydroxylgroup by means of which they may be incorporated into the polymer.

Preference is given to hexasubstituted ethanes, especially benzpinacoland the derivatives thereof, silylated pinacols, available commercially,for example, under the trade name ADDID 600 from Wacker, orhydroxyl-containing amine N-oxides, such as4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPOL).

Preference is given to dispersions in which, of the isocyanate groups ofthe compounds of component a),

from 0 to 70 mol %, preferably from 20 to 60 mol %, have been reactedwith isocyanate-reactive groups of at least one compound of componentc), and

from 2 to 10 mol %, preferably from 4 to 8 mol %, have been reacted withisocyanate-reactive groups of at least one compound of component d).

The remainder of the isocyanate groups, up to 100 mol %, essentiallycomprise blocked isocyanate groups. The ratio of blocked NCO equivalentsto free, NCO-reactive groups is preferably from about 2:1 to 1:2, inparticular about 1:1.

DE-A-198 60 041 also describes the implementation of the coating of thesubstrates, the implementation of the UV curing, which is advantageouslyeffected under an inert gas atmosphere, and the implementation of thethermal (heat) curing, where the addition of peroxide has been foundadvantageous. The coating techniques specified in German PatentApplication DE-A-198 60 041 also apply, mutatis mutandis, to coatingswith the polyurethane dispersions of the invention.

The substrates are generally coated by conventional techniques, known tothe skilled worker, in which at least one dispersion of the invention isapplied in the desired thickness to the target substrate and thevolatile constituents of the dispersions are removed. If desired, thisprocedure may be repeated one or more times. Application to thesubstrate can be made in a known manner, for example, by spraying,troweling, knifecoating, brushing, rolling, rollercoating orflowcoating. The coating thickness is generally in a range from about 3to 1000 g/m² and, preferably, from 10 to 200 g/m².

In general, the films formed on the substrate are cured by exposure tohigh-energy radiation, and thermally. The sequence of the curing stepsis arbitrary.

If desired, if two or more coats of the coating composition are appliedover one another, radiation curing may take place after each coatingoperation.

Radiation curing takes place preferably by exposure to high-energyradiation, i.e., UV radiation, or daylight, preferably light with awavelength from 250 to 600 nm, or by bombardment with high-energyelectrons (electron beams; from 150 to 300 keV). Examples of theradiation sources used are high-pressure mercury vapor lamps, lasers,pulsed lamps (flashlights), halogen lamps, or excimer emitters. In thecase of UV curing, the radiation dose which is usually sufficient forcrosslinking is in the range from 80 to 3000 mJ/cm².

If desired, exposure may also take place in the absence of oxygen, e.g.,under an inert gas atmosphere. Suitable inert gases are preferablynitrogen, noble gases, carbon dioxide, or combustion gases. Exposure mayalso take place with the coating composition covered with transparentmedia. Examples of transparent media are polymer films, glass, orliquids, e.g., water.

In one preferred technique curing is carried out continuously by passingthe substrate, treated with the formulation of the invention, atconstant speed past a radiation source. For this technique, the curingrate of the formulation of the invention needs to be sufficiently high.

This difference in the progress of curing over time may be exploited inparticular when the coating of the article is followed by anotherprocessing step in which the film surface enters into direct contactwith another article or is worked mechanically.

The advantage of the dispersions of the invention is that the coatedarticles may be processed further directly following radiation curing,since the surface no longer sticks. On the other hand, the precured filmis still sufficiently flexible and extensible that the article can bedeformed without the film flaking or tearing.

Even if deformation of the article is not intended, the technique, knownas dual cure, may prove advantageous, because the articles provided withthe precured film are particularly easy to transport and store, instacks, for example. Moreover, the dual cure technique offers theadvantage that the coating compositions are able to undergo chemicalaftercuring in dark regions (regions unaccessible to radiation) and,consequently, adequate material properties may still be achievedindependently of irradiation. Furthermore, spray mist deposits undergotack-free and emissions-free curing.

The invention additionally provides for the use of a dispersion, asdescribed above, to coat substrates of metal, wood, paper, ceramic,glass, plastic, textile, leather, nonwoven, or mineral buildingmaterials.

With particular preference, the dispersions of the invention aresuitable as or in exterior coatings, preferably of buildings or parts ofbuildings, road markings, and coatings on motor vehicles and aircraft.

The polyurethane dispersions of the invention are suitable withparticular advantage for coating substrates which can be coated attemperatures up to 160° C., especially metallic substrates such as ironor aluminum. The coating compositions of the invention exhibitparticular advantages in connection with their use as automotiveclearcoats.

Relative to similar known products, the aqueous polyurethane dispersionsprepared in accordance with the invention exhibit high scratchresistance in combination with good chemical resistance, good weatheringstability and good mechanical properties, and also good coatingsproperties in the unexposed regions.

The purpose of the examples which follow is to illustrate the invention,but not restrict it.

EXAMPLES

Unless specified otherwise, parts and percentages are by weight.

The stated contact angles were determined via the contact angle of adrop of water, as described in Adamson, Physical Chemistry of Surfaces,Chapter X, 5th Edition, Wiley, N.Y.

The hardness of the coating was determined as the pencil hardness, asdescribed in organic Coatings, Science and Technology, Vol. 2, p. 128,Wiley, N.Y. 1994. The loss of gloss was determined as specified inExample 2d).

The stated molecular weights were determined by gel permeationchromatography (polystyrene standard, eluent: tetrahydrofuran, UVdetection).

Example 1 Preparing a Dual Cure Polyurethane Acrylate Dispersion withBlocked Isocyanate Groups

1a) Preparing the Prepolymer:

A stirred vessel was charged with 455 parts of 2-hydroxyethyl acrylate,377 parts of 2,2-bis(4-hydroxycyclohexyl)propane, 2.3 parts of2,6-di-tert-butyl-p-cresol, and 1.2 parts of hydroquinone monomethylether, 0.5 part of dibutyltin dilaurate and 1500 parts of theisocyanurate of 1,6-hexamethylene diisocyanate were added, and themixture was stirred at 60° C. for 5 hours. Subsequently, it was dilutedwith 500 parts of acetone.

1b) Preparing the Aqueous Polyurethane Dispersion:

150 parts of the prepared solution were admixed with 1.4 parts ofthioglycolic acid, 1.6 parts of 2-butanone oxime and 1.8 parts oftriethylamine. The mixture was held at 40° C. for 8 hours. It was thendispersed in water and the acetone was removed by distillation.

1c) Preparing and Testing Coating Films:

The aqueous dispersion prepared was admixed with 4% of a mixture ofequal parts of benzophenone and 1-hydroxycyclohexyl phenyl ketone asphotoinitiator and applied to various substrates in coat thicknesses ofapproximately 40 μm. The films were flashed off overnight at roomtemperature, then heat-treated at 60° C. for 15 minutes and irradiatedwith two UV lamps (80 W/cm) on a conveyor belt at 10 m/minute. Thecontact angle was 62°. Subsequently, a coating film was heat-treated at150° C. for 15 minutes. Result: contact angle 74°; pencil hardness: 2 H.This shows that the hydrophilicity and hardness may be improved by theadditional heat treatment. The exposed and heat-treated coating filmsshowed no loss of gloss and no yellowing in the xenon test to DIN 53387(instrument: Xenotest 1200 from Heraeus, Hanau (DE)) after 1000 hours.

Comparative Experiment 1

The procedure of Example 1 was repeated but adding 1.2 parts of methanolinstead of 1.6 parts of 2-butanone oxime during the preparation of thepolyurethane dispersion. Following irradiation with UV lamps, thecontact angle was 62°; after the subsequent 15 minutes of heat treatmentat 150° C., it was 71° and the pencil hardness was 1 H.

Example 2 Preparing a Dual Cure Polyurethane Acrylate Dispersion WithExcess OR Groups and Separate Admixture of Blocked Isocyanates

2a) Preparing an Allophanate From Hexamethylene Diisocyanate and2-Hydroxyethyl Acrylate:

The preparation was as per DE-A-198 60 041, Experimental Section 1.1,Product No. 6. Under nitrogen blanketing, hexamethylene diisocyanate wasmixed with 40 mol % (based on the isocyanate) of 2-hydroxyethyl acrylateand the mixture was heated to 80° C. Following the addition of 200 ppmby weight (based on diisocyanate) ofN,N,N-trimethyl-N-(2-hydroxypropyl)ammonium 2-ethylhexanoate, thetemperature was slowly raised to 120° C. and held at this reactiontemperature. When the mixture had an isocyanate content of 13.5% byweight, the reaction was terminated by adding 250 ppm by weight ofdi(2-ethylhexyl) phosphate (based on diisocyanate). The reaction mixturewas then freed from unreacted hexamethylene diisocyanate in a thin-filmevaporator at 135° C. and 2.5 mbar. Following distillation, the producthad an NCO content of 13.5% by weight and a viscosity of 810 mPas at 23°C.

2b) Preparing the Prepolymer:

A stirred vessel was charged with 26 parts of 2-hydroxyethyl acrylate,0.2 part of 2,6-di-tert-butyl-p-cresol, and 0.1 part of hydroquinonemonomethyl ether. Then 0.02 part of dibutyltin dilaurate and 152 partsof the allophanate prepared as specified above from hexamethylenediisocyanate and 2-hydroxyethyl acrylate were added and the resultantmixture was stirred at 70° C. for 3 hours.

2c) Preparinq the Aqueous Polyurethane Dispersion:

Following the addition of 2.6 parts of thioglycolic acid, the mixturewas stirred at 70° C. for 3 hours more and cooled. It was diluted with100 parts of acetone, and 3.5 parts of triethylamine and 23 parts ofdiethanolamine were added. Subsequently, 50 parts of a 70% strengthsolution of the reaction product of dimethylpyrazole with theisocyanurate of isophorone diisocyanate, in methyl ethyl ketone, wereincorporated by stirring and 200 parts of water were added dropwise overthe course of 15 minutes. This gave a stable dispersion having aparticle size of 320 nm.

2d) Preparing and Testing Coating Films:

The dispersion prepared as per 2c) was mixed with 3% by weight of thephotoinitiator mixture specified in 1c), and this formulation was usedto prepare coating films on various substrates in a thickness ofapproximately 40 μm. The films were aerated overnight at roomtemperature and then heat-treated at 60° C. for 15 minutes. Thereafter,samples of the films were subjected to different curing conditions inExperiments A1, A2 and A3, namely:

Experiment A1: radiation curing with 2 UV lamps (80 W/cm) on a conveyorbelt at 10 m/min;

Experiment A2: curing in a drying oven at 150° C. for 30 minutes;

Experiment A3: radiation curing as A1, then curing as A2.

After curing operations A1 to A3, all films were physically dry and hadundergone through-curing (fingernail test).

The scratch resistance was assessed in a scrub test, in which 50 doublestrokes were performed using a Scotch Brite fabric under a weight of 750g. The degree of scratching was determined from the measurement of theloss of gloss (before and after scrubbing).

The loss of gloss for experiments A1 to A3 in the Scotch Brite test (50double strokes) was as follows: A1: 16; A2: 35; A3: 12.

Example 3 Preparing a Dual Cure Polyurethane Acrylate Dispersion withBlocked Isocyanates and OH Groups in Different Molecules

3a) Preparing the Prepolymer:

A stirred vessel was charged with 26 parts of 2-hydroxyethyl acrylate,0.2 part of 2,6-di-tert-butyl-p-cresol, and 0.1 part of hydroquinonemonomethyl ether. 0.02 part of dibutyltin dilaurate and 152 parts of anallophanate of hexamethylene diisocyanate and 2-hydroxyethyl acrylate(prepared as in Example 2a) were admixed and the mixture was stirred at70° C. for 3 hours.

3b) Preparing the Polyurethane Dispersion:

2.6 parts of thioglycolic acid were added, and the reaction mixture wasstirred at 70° C. for 3 hours more and cooled. The mixture was thendiluted with 100 parts of acetone, 3.5 parts of triethylamine and 23parts of diethanolamine were added, and 50 parts of a 70% strengthsolution of the reaction product of dimethylpyrazole with theisocyanurate of isophorone diisocyanate, in methyl ethyl ketone, wereincorporated by stirring, and 200 parts of water were added dropwiseover the course of 15 minutes. This gave a stable dispersion having aparticle size of 320 nm.

3c) Preparing and Testing Coating Films:

3% by weight of the photoinitiator mixture specified in Example 1c) weremixed into the polyurethane dispersion and the mixture was used to applycoating films with a film thickness of approximately 40 μm to a varietyof substrates. The films were aerated at room temperature overnight andthen heat-treated at 60° C. for 15 minutes. Subsequently, samples of theheat-treated films were cured as follows:

Experiment A4: radiation curing with 2 UV lamps (80 W/cm) on a conveyorbelt at 10 m/min;

Experiment A5: curing in a drying oven at 150° C. for 30 minutes.

After curing as per A4 and A5, the films were physically dry andthrough-cured (fingernail test). In the Scotch Brite test (50 doublestrokes) performed as in Example 2d), the loss of gloss was 16 forExperiment A4 and 35 for Experiment A5.

Example 4 Preparing a Dual Cure Polyurethane Acrylate Dispersion withBlocked Isocyanates and OH Groups in One Molecule

4a) Preparing the Prepolymer:

A stirred vessel was charged with 100 parts of an allophanate ofhexamethylene diisocyanate and 2-hydroxyethyl acrylate, prepared as inExample 2a), 0.13 part of 2,6-di-tert-butyl-p-cresol, and 0.1 part ofhydroquinone monomethyl ether. Following the admixture of 0.02 part ofdibutyltin dilaurate and 17.5 parts of 3,5-dimethylpyrazole, thereaction mixture was stirred at 70° C. for 3 hours.

4b) Preparing the Polyurethane Dispersion:

3.3 parts of thioglycolic acid were admixed to the reaction mixtureobtained, which was subsequently stirred at 70° C. for 3 hours more andcooled. The NCO content was 3%. Following the addition of 9.6 parts ofdiethanolamine and 4.4 parts of triethylamine, the mixture was dispersedin water.

4c) Preparing and Testing Coating Films:

The dispersion prepared in 4b) was mixed with 3% by weight of thephotoinitiator mixture specified in 1c) and used to prepare films with athickness of approximately 40 μm on black-colored glass plates, thefilms all having been aerated at room temperature overnight and thenheat-treated at 60° C. for 15 minutes. The film samples were then curedin Experiments A6 to A9 as follows:

Experiment A6: radiation curing on a conveyor belt at 10 m/min;

Experiment A7: curing in a drying oven at 150° C. for 30 minutes;

Experiment A8: curing as in A7 followed by radiation curing as A6;

Experiment A9: admixture of 3% by weight of tert-butyl benzoate,followed by curing as in A7.

The physically dry films obtained after curing had the following pencilhardnesses: A6: <6B; A7: <6B: A8: 3B; A9: 4B. It was found that byadmixing peroxides to the dispersion prior to curing them, the hardnessof the resulting cured films can be increased further. To assess thescratch resistance, the loss of gloss was measured in the Scotch Britetest (50 double strokes) as specified in Example 2d) for the filmsresulting from Experiments A6 to A9, with the following results: A6: 47;A7: 16; A8: 29; A9: 27.

Example 5 Preparing a Dual Cure Polyurethane Acrylate Dispersion WithBlocked Isocyanates and OH Groups in One Molecule With the Addition ofReactive Diluent.

The procedure of Example 4 was repeated but before the dispersion wasprocessed to films on black-colored glass plates it was admixed not onlywith 3% by weight of the initiator mixture specified in Example 1c), butalso 43% by weight of trimethylolpropane triacrylate as reactivediluent. After aeration overnight and subsequent 15-minute heattreatment at 60° C., the resultant films approximately 40 μm thick werecured as follows:

Experiment A10: 140° C. in a drying oven for 30 minutes, followed byradiation curing with 2 UV lamps (80 w/cm) in air on a conveyor belt at10 m/min;

Experiment A11: 140° C. in a drying oven for 30 minutes, followed byradiation curing with 2 UV lamps (80 W/cm) under nitrogen on a conveyorbelt at 10 m/min;

Experiment A12: radiation curing with 2 UV lamps (80 W/cm) in air on aconveyor belt at 10 m/min, then 140° C. in a drying oven for 30 minutes;

Experiment A13: radiation curing with 2 UV lamps (80 W/cm) undernitrogen on a conveyor belt at 10 m/min, then 140° C. in a drying ovenfor 30 minutes.

To assess the scratch resistance, the loss of gloss was determined inthe Scotch Brite test (50 double strokes) as specified in Example 2d)for the films resulting from Experiments A10 to A13, with the followingresults:

A10: 94; A11: 8; A12: 34; A13: 13. The addition of reactive diluent, andcuring under nitrogen, accordingly contribute to an increase in scratchresistance. The chemical stability of Experiment A13 was determined byway of the temperature above which damage to the surface occurred:

The values found—water >75° C., sulfuric acid 49° C., tree resin >75° C.and keratin 60° C.—demonstrate good resistance properties. The Erichsenflexibility (DIN 53156) is 4.5 mm.

Example 6 Dual Cure Polyurethane Dispersions with a Mixture ofIsocyanates

6a) Preparing an Allophanate from Hexamethylene Diisocyanate and2-Hydroxyethyl Acrylate:

Under nitrogen blanketing, hexamethylene diisocyanate was mixed with 40mol % (based on the isocyanate) of 2-hydroxyethyl acrylate and themixture was heated to 80° C. Following the addition of 200 ppm by weight(based on diisocyanate) of N,N,N-trimethyl-N-(2-hydroxypropyl)ammonium2-ethylhexanoate, the temperature was slowly raised to 120° C. and heldat this reaction temperature. When the mixture had an isocyanate contentof 13.5% by weight, the reaction was terminated by adding 250 ppm byweight of di(2-ethylhexyl)phosphate (based on diisocyanate). Thereaction mixture was then freed from unreacted hexamethylenediisocyanate in a thin-film evaporator at 135° C. and 2.5 mbar.Following distillation, the product had an NCO content of 13.5% byweight and a viscosity of 810 mPas at 23° C.

6b) Preparing the Aqueous Polyurethane Dispersion:

A stirred vessel was charged with 80 parts of the allophanate fromExample 6a), 20 parts of the isocyanurate of isophorone diisocyanate(Vestanat® T1890, from Hüls), 12.4 parts of decanediol, 0.13 part of2,6-di-tert-butyl-p-cresol, 0.1 part of hydroquinone monomethyl ether,and 0.03 part of dibutyltin dilaurate. Then 9.9 parts of hydroxyethylacrylate were added and the resulting mixture was stirred at 70° C. for3 hours. Following the addition of 2 parts of thioglycolic acid and 1.1parts of methanol, stirring was continued at 70° C. for 4 hours and thereaction mixture was then cooled. After 2.3 parts of triethylamine hadbeen added, the resultant product was dispersed in water.

Example 7 Polyurethane Dispersion with Added Reactive Diluent

The procedure of Example 6 was repeated but adding 30 parts ofdecanediol diacrylate prior to dispersion.

Example 8 Dual Cure Polyurethane Dispersion With Blocked IsocyanateGroups and Hydroxyl Groups In Different Molecules

A stirred vessel was charged with 140 parts of the allophanate fromExample 6a), 20 parts of the isocyanurate of isophorone diisocyanate(Vestanat® T1890, from Hüls), 17 parts of cyclohexane-1,4-dimethanol,0.2 part of 2,6-di-tert-butyl-p-cresol, 0.1 part of hydroquinonemonomethyl ether, and 0.04 part of dibutyltin dilaurate. Then 9.9 partsof triazole were added and the resulting mixture was stirred at 70° C.for 3 hours. Following the addition of 3 parts of thioglycolic acid and4 parts of methanol, stirring was continued at 70° C. for 4 hours andthe reaction mixture was then cooled. Then 3.8 parts of triethylaminewere added, the mixture was stirred at 70° C. for 0.5 hour, 41.6 partsof pentaerythritol triacrylate were added, and the resultant product wasdispersed in water.

The dispersions of Example 6-8 were admixed with 4% by weight of aphotoinitiator mixture comprising 1-hydroxycyclohexyl phenyl ketone andbenzophenone (Irgacure® 500 from Ciba) and applied to metal panels infilm thicknesses of approximately 40 μm. The films were flashed off atroom temperature overnight and subsequently heat-treated at 60° C. for15 minutes. The films were then subjected to radiation curing on aconveyor belt with a speed of 10 m/min using two UV lamps (80 W/cm) andto subsequent thermal curing in a drying oven at 150° C. for 30 minutes.The degree of scratching was determined from the loss of gloss (beforeand after appropriate stressing). The results of the scratch resistancetest are shown in Table 1. The chemical resistance was determined byapplying a droplet series of the corresponding chemicals to each paintedmetal panel and heating the panel in a temperature gradient oven. Table1 indicates the temperatures above which film damage occurred.

TABLE 1 Dispersion Scratch resistance from Ex. No. (loss in gloss/%)Chemical resistance 6 5.2 H₂SO₄: 42° C. Tree resin: 61° C. Water: 65° C.7 3.0 H₂SO₄: 47° C. Tree resin: 55° C. Water: 66° C. 8 9.0 H₂SO₄: 46° C.Tree resin: 50° C. Water: 49° C.

Example 9

Dual Cure Polyurethane Dispersion with a Mixture of Isocyanates

A stirred vessel was charged with 90 parts of the allophanate fromExample 6a), 10 parts of the isocyanurate of isophorone diisocyanate(Vestanat® T1890, from Hüls), 12.42 parts of decanediol, 0.13 part of2,6-di-tert-butyl-p-cresol, 0.1 part of hydroquinone monomethyl ether,and 0.03 part of dibutyltin dilaurate. Then 5.5 parts of 1,2,4-triazolewere added and the resulting mixture was stirred at 70° C. for 3 hours.Following the addition of 2 parts of thioglycolic acid and 5.3 parts oftrimethylolpropane, stirring was continued at 70° C. for 4 hours and thereaction mixture was then cooled. After 2.3 parts of triethylamine hadbeen added, the resultant product was dispersed in water. Performanceassessment was made by determining the scratch resistance and thechemical resistance, as described above for Examples 6-8. In addition,the hardness of the films was determined in accordance with DIN 50359and their yellowing by colorimetry in accordance with DIN 6174, 0°value. The results are likewise shown in Table 2. The dispersion of theinvention from Example 4 serves for comparison.

TABLE 2 Scratch Dispersion resistance from Ex. (loss of Hardness No.gloss/%) Chemical resistance (N/mm²) Yellowing 9 2.9 H₂SO₄: 44° C. 1463.5 Tree resin: 57° C. Water: 59° C. 4 8.5 H₂SO₄: <37° C. 139 6.8 Treeresin: <37° C. Water: <37° C.

As the results of performance testing show, the already good propertiesof the inventive dispersion 4 can be improved still further by using amixture of isocyanates.

Examples 10-12

Example 9 was repeated but replacing the decanediol by anothershort-chain diol. The results of performance testing are shown in Table3.

TABLE 3 Scratch Dispersion resistance from Diol (loss of Ex. No. Diolgloss/%) Chemical resistance 10 Hexanediol 4.4 H₂SO₄: 48° C. Tree resin:75° C. Water: 75° C. 11 HCP¹⁾ 7.4 H₂SO₄: 43° C. Tree resin: 38° C.Water: 43° C. 12 CHDM²⁾ 4.3 H₂SO₄: 42° C. Tree resin: 71° C. Water: 61°C. ¹⁾Bis(hydroxycyclohexyl)propane ²⁾Cyclohexanedimethylol

We claim:
 1. A UV- and heat-curable aqueous polyurethane dispersionsynthesized essentially from a) aliphatic polyisocyanates having an NCOfunctionality of from 2 to 4.5, b) compounds containing at least oneisocyanate-reactive group and at least one C═C double bondUV-polymerizable, in the presence of a photoinitiator, c) aliphaticcompounds containing at least two isocyanate-reactive hydroxyl,mercapto, primary and/or secondary amino groups, having a molecularweight of less than 500 g/mol, d) compounds containing at least oneisocyanate-reactive group and also at least one carboxyl group orsulfonic acid group, e) at least one basic compound for full or partialneutralization of the acid groups of the compounds d), f) an isocyanateblocking agent (f1) which converts isocyanate groups into blockedisocyanate groups with an unblocking temperature in the range from 70 to160° C., or addition of a low molecular mass compound (f2) containingblocked isocyanate groups, and g) if desired, a compound other thancompounds b) to f) which contains only one isocyanate-reactive group, the reaction products of a) with b) and c), prepared with astoichiometric excess of NCO groups in relation to hydroxyl groups,having been reacted with compounds d) and e) in amounts sufficient fordispersibility in aqueous medium, blocked isocyanate groups having beenintroduced into the molecule by reaction with isocyanate blocking agents(f1), or compounds (f2) containing blocked isocyanate groups having beenadded.
 2. A polyurethane dispersion as claimed in claim 1, comprisingcompounds b) as additive.
 3. A polyurethane dispersion as claimed inclaim 1, comprising in the polyurethane UV-polymerizable C═C doublebonds, hydroxyl groups, and blocked isocyanate groups.
 4. A polyurethanedispersion as claimed in claim 1, comprising compounds containingUV-polymerizable C═C double bonds and hydroxyl groups and compoundscontaining blocked isocyanate groups.
 5. A polyurethane dispersion asclaimed in claim 1, comprising compounds containing UV-polymerizable C═Cdouble bonds, aliphatic hydrocarbon diols incorporated via isocyanateand having a molecular weight of less than 500 g/mol, free hydroxylgroups, and compounds containing blocked isocyanate groups.
 6. Apolyurethane dispersion as claimed in claim 1, comprisingUV-polymerizable C═C double bonds and hydroxyl groups, synthesized fromaliphatic polyisocyanates containing isocyanurate, biuret or allophanategroups.
 7. A polyurethane dispersion as claimed in claim 1, whereincomponent a) comprises at least one compound Va) containing two freeisocyanate groups, at least one allophanate group and at least onefree-radically polymerizable C═C double bond, a carbonyl group or anoxygen atom in ether function being attached directly to the doublebond.
 8. A polyurethane dispersion as claimed in claim 7, wherein saidcompound Va) is selected from compounds of the formula IOCN—R¹R²—C(O)—R²—R¹_(n)NCO  (I) where n is an integer from 1 to 10, R¹is a divalent aliphatic or alicyclic C₂ to C₂₀ hydrocarbon unit or anaromatic C₆ to C₂₀ hydrocarbon unit, R² in each repeating unit is once—NH— and once

 R³ being a radical derived from an alcohol A by abstracting thehydrogen atom from the alcoholic hydroxyl group, said alcohol A furthercomprising at least one free-radically polymerizable C═C double bond,and a carbonyl group or an oxygen atom in ether attachment beingattached directly to the double bond.
 9. A polyurethane dispersion asclaimed in claim 7, wherein component a) comprises at least one compoundVa) and at least one further, different polyisocynate.
 10. Apolyurethane dispersion as claimed in claim 1, comprisingUV-polymerizable C═C double bonds and hydroxyl groups, synthesized fromthe allophanates of hexamethylene diisocyanate and hydroxyethyl acrylateand/or mixtures thereof.
 11. A polyurethane dispersion as claimed inclaim 1, comprising UV-polymerizable C═C double bonds and hydroxylgroups, synthesized from aliphatic polyisocyanates containingisocyanurate, biuret or allophanate groups, as building block a),hydroxyalkyl(meth)acrylates as building block b), aliphatic diols with amolecular weight of less than 500 g/mol as building block c), andmonothio or monohydroxy carboxylic acids as building block d).
 12. Apolyurethane dispersion as claimed in claim 1, comprising added reactivediluents.
 13. A polyurethane dispersion as claimed in claim 1,comprising added conventional coatings additives.
 14. A polyurethanedispersion as claimed in claim 1, containing UV-polymerizable C═C doublebonds and hydroxyl groups, comprising a photoinitiator in an amount offrom 0.1 to 5% by weight of its solids content.
 15. A polyurethanedispersion as claimed in claim 1, comprising at least one thermalinitiator.
 16. A polyurethane dispersion as claimed in claim 15, whereinsaid thermal initiator has a half life at 60° C. of at least one hour.17. A polyurethane dispersion as claimed in claim 15, wherein saidthermal initiator comprises at least one compound having at least oneisocyanate-reactive group which even after reaction with a compoundcontaining isocyanate groups is capable of releasing free radicals underheat.
 18. A polyurethane dispersion as claimed in claim 15, wherein saidthermal initiator comprises benzpinacol or a derivative thereof.
 19. Theuse of a polyurethane dispersion as claimed in claim 1 to coatsubstrates which can be coated at temperatures of up to 160° C.
 20. Theuse of a polyurethane dispersion as claimed in claim 1 to coatsubstrates comprising metal, wood, paper, ceramic, glass, plastic,textile, leather, nonwoven, or mineral building materials.
 21. The useof a polyurethane dispersion as claimed in claim 1 as or in exteriorcoatings, preferably of buildings or parts of buildings, road markings,or coatings on vehicles and aircraft.
 22. The use of a polyurethanedispersion as claimed in claim 1 as an automotive clearcoat.